Design And Control Of A Pneumatic Artificial Muscle-driven Lower Limb Exoskeleton Knee Joint

The lower limb exoskeleton robot is a highly integrated intelligent mechanical equipment,which is mostly used to help the aging population and the people with lower limb movement to walk or recover.The joints driven by pneumatic artificial muscles can achieve flexibility and safety from the source.It is the key basic functional component in the field of lower limb exoskeleton robot.As one of the most important joints in the whole lower limb exoskeleton robot,exoskeleton knee joint has always been a research hotspot.In this paper,you designed a compact and lightweight exoskeleton knee joint connecting rod structure.In order to improve the flexibility of the knee joint,the joint is driven by pneumatic artificial muscle.Because of the nonlinearity and hysteresis of the pneumatic artificial muscle,this paper designs an adaptive backstepping sliding mode control of the exoskeleton knee joint.The specific research contents of this paper are as follows :Firstly,the mechanism of human lower limb movement is analyzed.By comparing the advantages and disadvantages of the common pneumatic artificial muscle-driven joints,a knee joint structure with the advantages of the pulley mechanism and the lever mechanism driven by the pneumatic artificial muscle is designed.The exoskeleton knee joint structure is more compact and lighter,and the parameters of the exoskeleton knee joint structure are determined according to the working range of the pneumatic artificial muscle and the range of motion of the knee joint during normal walking.Secondly,through the summary of the existing pneumatic artificial muscle model,the mathematical model of the pneumatic artificial muscle used in this paper is determined,and the kinematics and dynamics modeling of the proposed exoskeleton knee joint structure is carried out to obtain the relationship between the exoskeleton knee joint driving torque and the structural parameters.The ADAMS simulation software is used for dynamic simulation to verify the correctness of the established dynamic model,which lays a foundation for subsequent control research.Then,by sorting out the mathematical model of pneumatic artificial muscle and the dynamic model of exoskeleton knee joint,the dynamic model of the whole exoskeleton knee joint system is obtained.Based on the dynamic model of exoskeleton knee joint system,sliding mode controller and adaptive backstepping sliding mode controller are designed.The simulation results verify the effectiveness of adaptive backstepping sliding mode control.Finally,based on the designed lower extremity exoskeleton joint driven by pneumatic artificial muscle,the control experiment design is carried out,and the experimental platform of exoskeleton knee joint system is built.The sliding mode controller and adaptive backstepping sliding mode controller designed in this paper are experimentally verified respectively.By comparing the two experimental results,it is proved that the adaptive backstepping sliding mode control has a good control effect on the exoskeleton knee joint driven by pneumatic artificial muscle.